A number of researchers argue that extremely processed foods are the reason behind rising rates of obesity, diabetes and other metabolic diseases. But others aren’t so certain.

Cookies and cakes from the grocery store are often highly processed. Does it matter? (Photo: Moving Moment / Shutterstock / NTB scanpix)

Ultra-processed food is a common term for heavily processed foods that typically contain substances rarely found in the kitchen.

These are industry-produced foods, and are often fortified with nutrients that would have been found in some of the original ingredients. They are often considered a hallmark of the Western diet.

Ultra-processed foods also often contain many substances that give them good taste, consistency and appearance, including colourants, flavour enhancers, emulsifiers and preservatives.

In other words: these types of foods are made from raw materials that are broken down and then reconstructed to create the products we eat.

Two Norwegian researchers have now summarized the research that explains how ultra-processed food can change the bacteria that live in our digestive systems, which then promote inflammation. The idea is that our eating habits, including consuming these kinds of foods, play a role in our ever-increasing problems with obesity and metabolic diseases.

But other researchers argue that we still have more to learn before we can come to this conclusion.

More ultra-processed foods

Studies from countries across the globe document how people are eating more and more ultra-processed foods. Investigations from the United States, Norway and several European countries show that more than half of the food we now buy is highly processed.

In the last 30 years, the number of people who are obese has increased dramatically in almost all countries in the world. Studies have also shown an explosion in metabolic diseases, such as type 2 diabetes.

Obviously, easy access to high-calorie foods and a daily routine that doesn’t include exercise play a role in these trends. But the general perception that gluttony and laziness are the whole explanation is not solidly supported by the science.

Several researchers have wondered if other factors in our environment, such as sleep habits or indoor temperatures, are playing a greater role than we think. Now ultra-processed food is being considered as another possible force behind these trends.

In the last issue of the academic journal Nutrients, Marit Zinöcker from Bjørknes University College and Inge Lindseth from Balderklinikken in Oslo summarize the research that has been done on possible relationships between heavily processed foods and obesity.

Connection between ultra-processed foods and obesity

Zinöcker explained that a research group at the university in São Paulo, led by Carlos Augusto Monteiro, started this line of investigation.

They created what was called the NOVA classification system, which groups food into four categories:

Unprocessed or minimally processed food

Processed culinary ingredients

Processed food

Ultra-processed food

Studies from Brazil showed that people who consumed up to half of their energy intake in the form of ultra-processed food were more likely to be obese.

Could explain strange data

If it is true that highly processed foods harm health, it could undeniably explain a lot of things.

"For example, it is typical that diet patterns associated with good health — such as the Mediterranean diet — are more often based on whole foods," says Zinöcker.

This trend can also be seen in different types of foods. For example, eating whole grains is associated with a lower risk of disease. But consuming processed grain products is associated with the opposite trend.

A Norwegian study of fish consumption also shows a similar tendency: Eating whole fish seems to be associated with less disease, while consuming processed fish products such as fish balls, fish sticks and fish cakes is linked to health problems.

No cause and effect

One of the problems with this type of information, however, is that a link between two phenomena does not say anything about causation. Current research doesn’t support the contention that ultra-processed food causes poor health.

It may be, for example, that people who eat a lot of ultra-processed foods also exercise less or live a more harmful lifestyle. Or that people who are concerned about their health are more likely to make their food from scratch.

The association between ultra-processed food and poor health may also be due to pure coincidence.

And even if it turns out to be true that ultra-processed food is actually the culprit, we still have no evidence that it is the processing itself that is the problem. It is still possible that the relationship between ultra-processed foods and poor health is due to the fact that ultra-processed foods often contain a lot of sugar, salt and fat, which on their own may adversely affect health.

A summary of research up to 2017 concluded that ultra-processed foods appear to be linked to obesity and an increased risk of heart disease, but also concludes that it is unclear as to what role the actual food processing plays.

Changing intestinal flora

In their review article, however, Zinöcker and Lindseth point out that changes in our intestinal flora, fed by the nutrients and substances in ultra-processed food, may explain the link between this type of food and the health problems that are associated with its consumption.

A recent commentary in the Norwegian Medical Association’s journal on internal medicine describes how intestinal flora can affect the body's own mechanisms in controlling its energy balance, such as the regulation of appetite or energy consumption.

But the most important thing may be bacteria's role in inflammation.

There is reason to believe that an adverse intestinal flora can cause inflammation, by making the intestines more permeable, for example. This may allow both intestinal bacteria and toxins they produce to leak into the bloodstream.

Several animal studies on food additives have shown that these substances can change intestinal flora to cause inflammation. Other research has shown that obese people have signs of inflammation in their body.

Jan Raa, professor emeritus in microbiology from the Arctic University of Norway, is intrigued by the idea that ultra-processed foods may have a hand in the increase in obesity and metabolic diseases. He cautions, however, that we should not be too wedded to the idea without being open to other explanations.

“In recent years, we’ve seen the intestinal microbial ecosystem gain a dominant place in the discussion of how nutrients affect the body,” he said. “That makes me think we need to be alert to other possible explanations.”